Modern mobile terminals, such as cellular telephones and personal communicators, are typically designed with an interface for connecting with external accessory devices. These accessory devices extend the functionality of the mobile terminal and/or provide other useful functions. Examples of accessories include battery chargers, headsets and “hands free” adapters (enabling the mobile terminal to be used without being held in the user's hand).
As can be appreciated, as the complexity of mobile terminals and their accessories have increased the required mobile terminal/accessory interface has increased in complexity as well. For example, the interface is typically required to accommodate the transfer of data between the mobile terminal and the accessory.
It is desirable that the mobile terminal/accessory interface be physically and electrically robust, be capable of handling low error rate data transfers, and yet still be low cost and of minimal complexity. Another important consideration is the power consumption of the mobile terminal/accessory interface. As in all battery powered devices, the minimization of power consumption is an important goal.
When using conventional accessory interfaces it has been problematic for the mobile terminal to detect certain specified accessories. Problems have also been observed using analog to digital converter (ADC)-based accessory detection schemes. Furthermore, with the ADC-based detection scheme there are only a limited number of accessories that can be identified (limited at least by the precision of the analog voltage that is produced to represent a given accessory, and by the conversion accuracy of the ADC in the mobile terminal).
Prior to this invention, all of the foregoing various and somewhat conflicting needs and goals have not been realized in circuitry that provides a mobile terminal/accessory interface, and the foregoing problems have not received a satisfactory resolution.
While described above in the context of mobile terminals, it should be appreciated that the same or similar problems can exist in other types of equipment.